It is known that speed bumps are generally raised elements installed on roads or streets designed to discourage and prevent vehicles from travelling at high speed by way of giving jolts to the vehicles travelling too quickly over the speed bumps. However, there are instances when a speed bump is undesirable. For example, speed bumps are not desirable on roads where emergency vehicles frequently travel.
Several retractable speed bumps have been developed. U.S. Pat. No. 4,342,525 (Mastronuzzi, Jr.) discloses a retractable speed bump mounted in a street, road, or roadway for controlling the speed of vehicles, which includes a generally rectangularly-shaped encasement containing upper and lower, relatively movable, wedge-shaped members slidably fitted in the encasement and configured to cooperate by means of friction-reducing means such as ball bearings in adjacent, inclined faces to selectively raise the top of the upper member above street or road level responsive to activation of a hydraulic cylinder attached to the encasement and the lower member.
U.S. Pat. No. 4,974,991 (Mandavi) discloses a speed bump device which allows a vehicle to roll over the device slowly with little resistance. The speed bump device is provided with a lock which operates to lock the speed bump of the device in operative position when contacted by a vehicle wheel moving at a higher speed, thereby causing an appreciable bump effect. The speed bump device is also provided with a frame having a transverse bump bar at its upper end and a counterweight bar at its lower end. The frame is rotatably mounted by transverse axles secured to opposite sides of an open-topped container. In the resting position, the bump bar projects up above the open top. A lock arm projects rearwardly from and is rigidly interconnected to the frame for rotation therewith. It bears a vertical pendulum arm which rotates forwardly and rearwardly and which has a friction block at its lower end. A second friction block is mounted in the container below and to the rear of the first friction block. The two blocks contact and lock together to prevent continued rotation of the frame only when the bump bar is struck with sufficient force by a fast travelling vehicle wheel to swing the first friction block into the second block as the frame rotates. As a result, the bump bar remains up above the container to transmit a large bump to the vehicle, with the frame being locked in place.
U.S. Pat. No. 5,509,753 (Thompson) discloses a motorized retractable speed bump or warning device wherein the raising and lowering of the retractile is controlled by multiple remote means from signals generated by traffic conditions. The motorized retractable speed bump, wherein a retractile comprising of bi-folding hinged plates, which are elevated to present a visible obstruction to motor vehicles, and a position restraining device, operated by rotary and or linear motor drive means, by on/off manual push button switching, or through a series of Programmable Logic Controllers, by way of analogue or digital signals emanating from permanently mounted speed detecting devices.
The above-mentioned speed bump devices are unsuitable for use on roads and streets where heavy vehicles and vehicles carrying heavy loads travel.